1. Field of the Invention
This invention is related to a semiconductor integrated circuit wherein the power supply voltage supplied from the outside is stepped down internally of the integrated circuit for use as the internal power supply voltage.
2. Description of the Related Art
In a semiconductor integrated circuit in which a large number of elements are integrated (hereinafter referred to as IC) such as a static semiconductor memory (hereinafter referred to as SRAM), the size of transistors is increasingly reduced year each year. As a result, if the standard power supply voltage of 5 V which has traditionally been used is supplied to an IC, a reliability problem such as destruction of the internal micronized transistors occurs.
Conventionally, in a highly integrated IC in which such a problem can occur, internal stepdown circuit 91 is provided, as shown in FIG. 1, and after a standard power supply voltage V.sub.EXT of 5 V supplied from the outside is stepped down in the internal stepdown circuit 91 to an internal power supply voltage V.sub.INT of the order of 3 V, for instance, it is provided to internal circuit 92 including the micronized transistors.
Incidentally, no problem occurs if the conventional IC is always operated by the standard power supply voltage of 5 V obtained in a power supply unit. However, if the IC is a SRAM and a so-called battery backup operation causing data to be held by a battery is performed, a problem occurs. That is, up to present, a current is consumed in internal stepdown circuit 91 not only in the operation by the power supply voltage obtained in the power supply unit, but also in the backup operation by a battery. For this, the consumption of the battery becomes extreme and the battery backup operation for a long period of time is not available.